Since the advent of a resist for KrF excimer laser (248 nm), a pattern forming method utilizing chemical amplification is used so as to compensate for sensitivity reduction due to light absorption. For example, in the positive chemical amplification method, first, a photoacid generator contained in the exposed area decomposes upon irradiation with light to generate an acid and in the course of baking or the like after exposure (PEB: Post Exposure Bake), an alkali-insoluble group contained in the photosensitive composition is changed into an alkali-soluble group by the catalytic action of the acid generated. Thereafter, development is performed using, for example, an alkali solution, whereby the exposed area is removed and a desired pattern is obtained (see, for example, Japanese Patent No. 3632410, JP-A-2011-100105 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2009-274963 and Japanese Patent No. 5001192).
As for the alkali developer used in the method above, various developers have been proposed. For example, as the alkali developer, an aqueous alkali developer of 2.38 mass % TMAH (aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Miniaturization of a semiconductor device has lead to a progress in shortening the wavelength of the exposure light source and increasing the numerical aperture (higher NA) of a projection lens, and an exposure machine using an ArF excimer laser having a wavelength of 193 nm as the light source has been so far developed. As a technique to more increase the resolution, a method of filling the space between the projection lens and the sample with a high refractive-index liquid (hereinafter, sometimes referred to as “immersion liquid”) (that is, an immersion method) has been proposed. Furthermore, EUV lithography of performing exposure to ultraviolet light with a shorter wavelength (13.5 nm) has also been proposed.
In recent years, a pattern forming method using an organic solvent-containing developer is also being developed (see, for example, JP-A-2008-281975, JP-A-2010-139996, JP-A-2010-164958 and JP-A-2011-203644).